Dynamoelectric machines conventionally include stacks of laminations made up of magnetic material as part of the core of their rotor construction. In many cases, heat is generated in the lamination stack of the core as a result of eddy currents induced by magnetic fields generated during operation of the machine or as a result of hysterisis losses. Further, if the rotor is provided with an electrical winding or conductor bars, the lamination stack may be heated as a result of heat transfer from the electrical windings or conductor bars which heat up during the operation of the machine as a result of I.sup.2 R losses. Over the years, many efforts have been made to prevent motor cores from overheating. For example, the use of stacks of laminations itself is employed to reduce eddy current losses which in turn reduces the heat generated in the rotor. Moreover, it is common to include a fan on the rotor shaft for drawing or propelling the coolant, typically ambient air, across machine components including the lamination stack. In this regard, it has also been conventional to provide coolant passages in the lamination stack and to flow a coolant that may range from ambient air to oil to a refrigerant through such passages for cooling purposes.
In a problem unrelated to cooling, the laminations must be mounted onto a rotor shaft after they are assembled to form a core. Grinding of the inside diameter of the assembled core and the outside diameter of the rotor shaft is often required to provide an acceptable interference fit between the inside diameter of the core and the outside diameter of the rotor shaft. One known approach to eliminate the requirement for grinding is to provide a dimpled or lobed inner periphery for the core. Because the lobes are more easily deformed than a continuous inside cylindrical surface, the core and the shaft can accommodate a broader range of manufacturing tolerances to provide an acceptable interference fit, thereby eliminating the requirement for grinding.